The objective of this research is to describe inputs to the simian oculomotor nuclei from three anatomically verified sources: the vestibular nuclei, the pontine and mecencephalic reticular formations and the cerebellum. About half of the units recorded in the vestibular nuclei respond only to horizontal oscillations of the head with a discharge pattern correlated with head velocity. The remaining half discharge not only to head oscillations but also to eye movements; these units either pause for saccades in all directions or increase their steady firing rates for increasing eye deviations. Units in the surrounding reticular formation have discharge patterns similar to those in the vestibular nuclei. Single cells in the fastigial nuclei also respond to head oscillations but their discharge pattern, in addition to having a strong component proportional to head velocity, is also a function of head acceleration. Fastigial cell activity is not modulated by eye movements. Units in the flocculus with a vestibular sensitivity exhibit a much greater vestibular modulation of activity with the monkey fixating an object oscillating at the same velocity as his head then when the monkey has no fixation target in the dark.